1. Field of the invention
This invention relates in general to pumps for injecting fluids into a well, and in particular to a multistage centrifugal pump.
2. Description of the Prior Art
In oil field applications, frequently, water must be pumped down an injection well. This may occur for disposal or for maintaining or increasing reservoir pressure in enhanced recovery operations. Various types of pumps are employed at the surface for injecting the water into the well at a high flow rate.
In one prior art type, a multistage centrifugal pump will be mounted horizontally at the surface adjacent the well. The centrifugal pump is of a type that normally would be utilized in a vertical application within a well for pumping fluid from the well. When used as an injection pump, however, the prior art centrifugal pump is driven by a conventional electrical motor.
A special thrust bearing locates at the end of the pump for handling the thrust due to the discharge of fluid from each of the impeller and diffuser stages. An intake chamber surrounds the intake of the pump. A feed pump will supply water under pressure from a tank to the intake chamber. While this type of pump works well, it requires some special components, such as the thrust bearing and intake chamber.
Also, if the feed pressure is high, a large differential will exist between the intake chamber and the atmosphere. The shaft extends out of the intake chamber into the atmospheric pressure. High pressure seals around the shaft are required. Sealing under high pressure around the rotating shaft is a problem. Consequently, these types of pumps are not very suitable for boosting a fairly high feed pressure to a higher pressure.
Another problem that can occur in horizontally mounted injection pumps results from gas contained in the feed fluid. Gas within the water detracts from the performance of the pump. Gas separators are used downhole when used as a well pump, but are not normally used on the surface for injection pumps.
Pumps have been installed in shallow vertical wells or sumps in the past for pressure boosting applications. In those instances, a liner is employed in the well. The liner has an open lower end surrounds the pump, seal section and motor. The liner forces fluid pumped by a feed source into the well to flow up around the motor to the intake of the pump. These assemblies require the expense of a well, and are more expensive to pull for maintenance than a horizontally mounted surface pump.